Chargeless electrophotographic printing process

ABSTRACT

The present invention provides an electrophotographic printing process comprising the steps of forming a first radiation energy pattern on an electrophotosensitive material without previously imparting a charge thereon, to form a latent electrical image on the electrophotosensitive material, forming a second radiation energy pattern to control the latent image, and thereafter causing the latent image to become visible by developing it with a charged, fine particle developer.

United States Patent [56] References Cited UNITED STATES PATENTS 7/1958 Kallman Eiichi lnoue;

lchiro Endo, Tokyo; Kunihiro Fukushirna, Kawasaki-shl, all of Japan [72] Inventors [21] AppLNo. [22] Filed 5/1959 Gundlock...... May 191967 2,955,938 10/1960 Steinhelper [45] Patented Oct. 26,1971 2 979 403 4/1961 ,Giaimo [73] Assignee Canon Camera KabushikiKalsha 2990280 6/1961 Tokyo, Japan 3,057, [3%] Pr1or1t1es May 26, 1966 3 206 gz g [3 1 Japan [31] 41/339; 3,249,430 5/1966 Metcalfe et a1. May 26, 1966, Japan, No. 41/33986; May Primary Examiner-George F. Lesmes 26, 1966, Japan, No. 41/313987 Assistant Examiner-John C. Cooper, 111

Attorney-Ward, McElhannon, Brooks & Fitzpatrick [54] SE E% %E g ABSTRACT: The present invention provides an electrophoto- 17 Claims 12 Dram m 5 graphic printing process comprising the steps of forming a first g g radiation energy pattern on an electrophotosensitive material [52] US. without previously im arting a char e thereon, to form a 96/1, 1 17/37 LE G03g 13/22 latent electrical image on the electrophotosensitive material, forming a second radiation energy pattern to control the latent image, and thereafter causing the latent image to become visible by developing it with a charged, fine particle developer.

PATENTEDum 26 I87! SHEET 2 [IF 5 PATENTEDucT 26 197i SHEET 3 [IF 5 it I it: 1 t l PATENTEBum 2s IHYI 3,615,383

SHEET w 5 CIIARGELESS ELECTROPIIOTOGRAPIIIC PRINTING PROCESS The present invention relates to an electrophotographic printing process, and particularly, relates to an improvement of the method of chargeless electrophotographic printing.

A chargeless electrophotographic printing process in which a radiation energy pattern is applied to an electrophotosensitive material which has not been previously charged, to form an electrical latent image which is then developed using charged fine particle developer has been previously known. Such a method is disclosed in Japanese Pat. No. 278,767. However, in this process, the electrical latent image when developed does not have the charged fine particles attached only to the image portion, but also to the nonimage portion, i.e. the portion out of image portion; which results in fogging. Furthermore, it is difficult to obtain a good positive image from such a negative original. Additionally in this prior process, when the energy pattern is applied to the photosensitive layer through the negative original, in development, negatively charged developer particles attached selectively to the portion where'the energy pattern was applied, while positively charged developer particles attached to the portion where the energy pattern was not applied. In other words, for obtaining the fonner positive image and the latter reversed image, it was necessary to conversely use the charged fine particle developers of different polarities and the operation was therefore highly complex.

An object of the present invention is to overcome the above-mentioned defects and present an improved printing process.

Another object of the present invention is to provide an electrophotographic printing process which obtains a desired image by applying a first radiation energy pattern to the electrophotosensitive material to form an electrical latent image thereon, and applying a second radiation energy pattern to the body to control the latent image.

Another objm of the present invention is to provide an electrophotographic printing process whereby a high contrast fogless image is obtained by applying a first radiation energy pattern to a first surface of the electrophotosensitive material to form an electrical latent image, and applying a second radiation energy pattern to a second surface, opposite to the first surface, to control the latent image.

Another object of the present invention is to provide an electrophotographic printing process to obtain a high contrast reversed image, which is negative when the original is negative and visa versa; by applying a first radiation energy pattern to a first surface of the electrophotosensitive material to form an electrical latent image thereon, and applying a second radiation energy pattern to the same first surface to control the latent image.

A further object of the present invention is to provide an electrophotographic printing process to optionally form a positive, which is positive when the original is negative but becomes negative when the original is positive; or its reversed image by forming latent positive and reversed images, respectively, on the photosensitive layer and the surface of the supporting body, and thereafter using a charged particle developer of the same polarity to selectively make visible the desired one of said positive and reversed latent images.

The above-mentioned and other objects and advantages of the present invention are apparent from the following description which refers to the illustrative embodiments shown in the attached drawing, in which:

FIGS. 1-6 show illustrative embodiments, respectively, of the first class of the present process in which a first radiation energy is applied to a first surface of the electrophotosensitive material to form an electrical latent image and a second radiation energy pattern is applied to a second surface, opposite to said first surface, to control the latent image. FIG. I shows the case in which a first radiation energy pattern in accordance with the original light-and-dark pattern, is applied to the photosensitive layer of the electrophotosensitive material and then a uniform second radiation energy pattern is applied to the electrophotosensitive material from the side of the supporting body thereof. FIG. 2 shows the case in which a uniform first radiation energy pattern is applied to the electrophotosensitive material from the side of the supporting body thereof and then a second radiation energy pattern, in accordance with the original light-and-dark pattern, is applied to the electrophotosensitive material from the side of the photosensitive layer thereof. FIG. 3 shows the case in which a first radiation energy pattern, in accordance with the original light-and-dark pattern, is applied to the surface of the photosensitive layer of the electrophotosensitive material and at the same time a uniform second radiation energy pattern is applied from the side of the supporting body of the electrophotosensitive material. FIG. 4 shows the case wherein a first radiation energy pattern, in accordance with the original light-and-dark pattern, is applied to the electrophotosensitive material from the side of the supporting body thereof, and then a uniform second radiation energy pattern is applied to the electrophotosensitive material from the side of the photosensitive layer. FIG. 5 shows the case in which a uniform first radiation energy is applied to the photosensitive body from the side of the photosensitive layer and thereafter a second radiation energy pattern, in accordance with the original light-and-dark pattern, is applied to the electrophotosensitive material from the side of the supporting body. Finally, FIG. 6 shows the case wherein a first radiation energy pattern, in accordance with the original light-and-dark pattern, is applied to the electrophotosensitive material from the side of supporting body of the electrophotosensitive material and at the same time a uniform second radiation energy is applied to the photosensitive body from the side of the photosensitive layer thereof; and

FIGS. 7-12 show illustrative embodiments, respectively, of the second class of the present process in which a first radiation energy pattern is applied to a first surface of the electrophotosensitive material to form an electrical latent image thereon and a second radiation energy pattern is applied to the same surface of said first surface to control the latent image previously formed thereon. FIG. 7 shows the case in which a first radiation energy pattern, in accordance with the original light-and-dark pattern, is applied to the photosensitive layer of the electrophotosensitive material to form an electrical latent image thereon, and a second radiation energy pattern, of the same original light-and-dark pattern, is applied to the same surface. FIG. 8 shows the case wherein a first radiation energy pattern, in accordance with the original light-and-dark pattern, is applied to the electrophotosensitive material from the side of photosensitive layer and thereafter a uniform second pattern is applied from the side of the photosensitive layer. FIG. 9 shows the case whereby a uniform first radiation energy pattern is applied to the electrophotosensitive material from the side of the photosensitive layer and a second radiation energy pattern, in accordance with the original light-anddark pattern, is applied from the same side. FIG. to shows the case in which a first radiation energy pattern, in accordance with the original light-and-dark pattern, is applied to the electrophotosensitive material from the side of the supporting body to form an electrical latent image and thereafter a second radiation energy pattern, in accordance with the same original light-and-dark pattern, is applied to the same surface. FIG. 11 shows the case wherein a first radiation energy pattern, in accordance with the original lightand-dark pattern, is applied to the electrophotosensitive material from the side of the supporting body and thereafter a uniform second radiation energy pattern is applied from the same side. Finally, FIG. 12 shows the case in which a uniform first radiation energy pat tern is applied to the electrophotosensitive material from the side of the supporting body, and thereafter a second radiation energy pattern, in accordance with the original light-and-dark pattern, is applied from the same side.

The electrophotographic printing process according to the present invention comprises supplying a first radiation energy pattern, without having previously charged the electrophotosensitive material, to the electrophotosensitive material to form thereon an electrical latent image, supplying a second radiation energy pattern to the electrophotosensitive material to control the latent image, and causing the controlled latent image, and causing the controlled latent image to become visible via development in a charged fine particle developer to obtain a high contrast, fogless image or a reversed image, when a like polarity developer is utilized.

IN the detailed explanation below, the electrophotographic printing process of the present invention is classified into two types. This classification depends upon the surfaces of the electrophotosensitive material on which the first and second radiation energy patterns are applied.

The first class of the present process is shown in FIGS. 1-6, in which a first radiation energy pattern is applied to the electrophotosensitive material from a first surface, e.g. from the photosensitive layer side or the support side, to form an electrical latent image thereon; and a second radiation energy pattern is applied to the electrophotosensitive material from its second surface, which surface is opposite to the first surface through which the first radiation energy pattern was applied, e.g. when the first surface is the supporting body then the second surface is the photosensitive layer or visa versa, to control the latent image. The second class of the process disclosed in the present invention is shown in FIGS. 7-12, in which a first radiation energy pattern is applied to the electrophotosensitive material from its first surface, e.g. from the side of the photosensitive layer or supporting body, to form an electrical latent image thereon; and thereafter a second radiation energy pattern is applied through the same surface, the first surface through which the first radiation energy pattern was applied, to control the latent image.

The first and second classes of the present process are further classified into three groups according to the nature of the first radiation energy and second radiation energy pattern. The first group is shown in FIGS. 1, 3, 4, 6, 8 and 11, and is present when the first radiation energy pattern is in accordance with the original light-and-dark pattern, and the second radiation energy pattern is a uniform energy pattern. The second group is shown in FIGS. 2, 5, 9 and 12, and is present when the first radiation energy pattern is a uniform radiation energy pattern and the second radiation energy pattern is in accordance with the original light-and-dark radiation energy pattern. Finally, the third group is shown in FIGS. 7 and 10, and is present when both the first and second radiation energy patterns are in accordance with the original light-anddark radiation energy pattern.

In this invention, the control of the electric latent image is defined to reverse the surface potential at the light-and-dark areas of the latent image obtained by the exposure through an original, or to make the surface charges at the light-and-dark areas opposite to each other.

In each of the above-mentioned classes, the electrical latent image formed on the electrophotosensitive material is developed by the action of charged color particles present in the photosensitive layer surface or the supporting body surface, provided the latter surface satisfies the conditions hereinafter specified as necessary to make visible the latent image.

The developing method in the present printing process may be a conventional one but it is preferable to use a liquid developing agent containing the charged fine particle toner.

The electrophotosensitive material of the present invention comprises a photosensitive layer coated on a supporting body, however, when the photosensitive layer is a film having an organic semiconductor dispersed therein via a bonding agent or is made of an inorganic semiconductor manufactured into a cellulose fiber, the supporting body is unnecessary.

The substance constituting the photosensitive layer of the present invention has a property which manifests electrical conductivity which varies according to an electromagnetic wave. For example, N-type inorganic semiconductors such as ZnO, TiO,, Al,0,, CdS, ZnSe, CdSe and ZnCdS: P-type inorganic semiconductors such as Se, SeTe, CuO, and NiO; organic semiconductors such as anthracene, polyvinylcarbazole, pyrene, ovalene and any]; metal or organic metal salts such as Al, Pt and Ag; and organic memory coding (O.M.C.) are preferably used for the invention. Furthermore, it is preferable that the photosensitive layer have a dark resistivity above IOKI-cm. for holding the charge. The supporting body may be Al, Al laminated paper, paper, glass, mylar, polyethylene and other synthetic resins, tracing paper, or other materials conventionally used can be utilized in the present invention, however; it is preferable to use the substances having a resistivity above lOWl-cm. In the embodiments of the invention where the energy pattern is applied to the electrophotosensitive material from the side of the supporting body, it is preferable that the supporting body be made of transparent or semitransparent substances, however; visually opaque substance can be used where the thickness thereof permits the penetration of the electromagnetic wave. The thickness of the supporting body is determined by the type of substance and elecromagnetic wave to be used. In the experiments conducted, the thickness utilized was about 8011.. Where an electrical latent image was developed at the surface of the supporting body, the preferable support from an experimental viewpoint had a resistivity which ranged from 10 to lO(l-cm., a thickness below 4011., and was made of material such as cyanoethylcellulose, methylcellulose, ethylcellulose and so on of cellulose series.

Light rays and thermal rays are preferably used as the energy for the present invention; and electron rays, X-rays and 'yrays of an electromagnetic wave were actually used. The amount of energy utilized to carry out the instant process differs in each case dependent on which process is employed and the type of substances used for the photosensitive layer and the supporting body. The magnitude of the required energy should be determined to satisfy the most suitable condition for each case.

The means for imparting energy are not limited to the one shown in the drawing, i.e. the energy pattern is projected without use of an optical system; but any conventional means can be used and these means can include an optical system therein.

Referring to the drawing, FIGS. 1-6 show the first class of the present process, in which a'first radiation energy pattern is applied to a first surface of the electrophotosensitive material to form an electrical latent image, and successively or simultaneously a second radiation energy pattern is applied to a second surface, opposite to the first surface, of the electrophotosensitive material to control the latent image. In the figures, I indicates the photosensitive layer, 2 is a supporting body or layer, both of which constitute the electrophotosensitive material 3, 4 indicates the original light-and-dark pattern normally consisting of a negative film, 5 indicates the charged particles attached to the electrical latent image, and I0 and 11, respectively, show energy sources.

The first step of the process shown in FIG. I, as seen in FIG. lI, is the application of first radiation energy, according to the light-and-dark pattern of the original 4 which is in close contact with the photosensitive layer 1 of the electrophotosensitive material 3, to the layer I by the light source 10 to form an electrical latent image on the layer 1. The second step, as seen in FIG. 1-2, is the application of a unifonn second radiation energy pattern to the side of the supporting body 2 by light source 11 to control the latent image previously formed. It is preferable to maintain the relationship that, the amount of the energy, according to the original light-and-dark pattern, absorbed by the photosensitive layer should be larger than the amount of the uniform energy absorbed by the photosensitive layer. This relationship is common to all of the processes of the present invention described hereinafter. On the electrophotosensitive material, the static charge patterns are formed as shown in FIGS. l-l and 1-2, by and notations, respectively, with the result that the latent image after being controlled has high contrast. Thereafter, the controlled latent image is developed by a charged fine particle developer. Where the development is made at the photosensitive layer and the charged fine particles have a negative charge, these particles are attached to the portion where light was applied to obtain a positive visual image 5, (FIG. ll-El). Where the fine particles are positively charged, a reversed image is obtained. The above explanation assumes the case where the photosensitive layer is an N-type semiconductor such as ZnO. Where, however, P-type semiconductor is used, such as Se, the charged pattern obtainable is reversed. Furthermore, as seen from FIG. ll-d, when the development is made on the surface of the supporting body, the image 5, is reversed with respect to the image shown in FIG. l1-3. In the case of FIG. ll-d, it is preferably that the supporting body have a resistivity of about l to IO II-cm. and a thickness less than 20p. In the processes explained hereinafter it is preferable to satisfy the above condition when the development is made on the supporting body. 7

The first step of the process shown in FIG. 2, as seen in FIG. 2-1, is the application of a uniform first radiation energy pattern by the light source Ill to the whole surface of the supporting body 2 of the electrophotosensitive material 3 to form an electrical latent image on the photosensitive layer 2. The second step of the FIG. 2 process, as seen in FIG. 2-2, is the application of a second radiation energy pattern, according to the light-and-dark pattern of the original 4i which is in close contact with the photosensitive layer I, this pattern is applied with the aid of the light source lid to control said latent image. The static charged patterns are formed on the electrophotosensitive material by these first and second steps as, respectively, shown in the figures. Therefore, the controlled latent image has a high contrast. This controlled latent image is then developed and made visible by the same process as is shown in FIG. I and as the result thereof, visual images of 5 and 5, are obtained as shown in FIGS. 2-3 and 2-4, respectively.

The initial step of the process shown in FIG. 3, as seen in FIG. 33-11, is the application of a first radiation energy pattern, according to the light-and-dark pattern of the original 4 which is in close contact with the photosensitive layer ll of the electrophotosensitive material 35, to the photosensitive layer I by the light source III. This initial application forms an electrical latent image on the photosensitive layer. At the same time, a uniform second radiation energy pattern is applied from the support side of body 2 by the light source I11, this second pattern is utilized to control the latent image. During the dual application step (FIG. El -ll), the static charge pattern shown in the drawing is obtained on the electrophotosensitive material, and consequently, the controlled electrical latent image has a high contrast. Thereafter, the controlled image is developed, and made visible in the manner shown in FIG. 1. Thus the visual images 5 and 5 shown in FIGS. 3-2 and 3-3), respectively, are obtained.

In the processes shown in FIG. I to FIG. 3, one radiation energy pattern was applied to the photosensitive layer I, according to the light-anddark pattern of the original. In the following processes of FIGS. to 6, a radiation energy pattern, according to the original light-and-dark pattern is applied to the electrophotosensitive material from the side of the supporting body.

The first step of the process of FIG. d, as shown in FIG. d-I, is the application of a first radiation energy pattern, according to the light-and-dark pattern of the original 4} which is in close contact with the supporting body 2, to the body 2 by the light source lltl to form an electrical latent image on the photosensitive layer. In the second step, as shown in FIG. 4-2, a uniform second radiation energy pattern is applied to the whole surface of the photosensitive layer by the light source II. This second pattern is used to control the latent image. During these two steps, the static charge patterns shown in FIG. 41-11 and 3-2, respectively, are obtained. Accordingly, the controlled latent image has high contrast. Thereafter, the controlled latent image is developed in the same manner as specified in the process of FIG. I, to obtain visual images 5,, and 5 as shown in FIGS. il-3 and ti-4i, respectively. The difference between the process of FIG. 4 and the processes of FIGS. 11-3 is that when the same charged particle developer is used, a reversed image is formed on the photosensitive layer side while the positive image is formed on the supporting body side. This assumes that the original is a negative. This relationship also holds true in the processes of FIGS. 5 and 6.

In the process of FIG. 5, the first step, as seen in FIG. 5-1l, is the application of a uniform first radiation energy pattern to the electrophotosensitive material from the side of the photosensitive layer I to form an electrical latent image thereon. The second step, as seen in FIG. 5-2, is the application of a second radiation energy pattern, according to the light-and-dark pattern of the original 3 which is in close contact with the supporting body 2, to the supporting body 2 via the light source III. During these steps, the static charged patterns are formed on the photosensitive body, respectively, as shown in FIGS. 5-1 and 5-2. Thus the controlled latent image again has a high contrast. The controlled latent image is thereafter developed in the same manner as specified in the discussion of FIG. 4 and visual images 5 and 5 as shown in FIGS. 5-3 and 5- 3, are obtained.

In the process of FIG. 6, the first step, as seen in FIG. tit-ll, is the application of a first radiation energy pattern, according to the light-and-dark pattern of the original d which is in close contact with the supporting body 2, to the supporting body by the light source It) to form an electrical latent image on the photosensitive layer 2. At the same time, a uniform second radiation energy pattern is applied to the whole surface of the photosensitive layer to control the latent image. During these steps, the static charge patterns are formed on the electrophotosensitive material as shown in FIGS. (6-11, and consequently, the controlled latent image has high contrast. This controlled latent image is then developed in the same manner as described in the description of FIG. 6 to form visual images 5 and 5 as shown in FIGS. 6-2 and 6-3, respectively.

In the above-mentioned processes of FIGS. 1-46, the formed latent images have high contrast, so that the visual images produced therefrom are also of high contrast and unfogged. Furthermore, the time necessary for the development is significantly shortened.

The following are examples of the processes shown in FIGS. 11-6, which belong to the first class of the present invention.

EXAMPLE 1 Ten gr. of ZnO (manufactured by SAIiAI IfAGAItU INK.) and 2 gr. of alkyd resin (trade name Olester 301) and I3 ml. of toluene were mixed in a ball mill for about 3%; hours to obtain an emulsion. This emulsion was coated on a transparent polyethylene film base having a thickness of about 3041. to form an electrophotosensitive material of ZnO-alkyd resin series. The thickness of the coated emulsion varied from I0,u to 20p" An original consisting of a negative film, was then placed in close contact with the surface of the photosensitive layer of the body. A first radiation energy pattern, according to the light-and-dark pattern of the original, was then applied to the photosensitive layer during one-ninetietlh of a second interval to form an electrical latent image on the photosensitive layer. The energy source utilized was by way of example a I50 watt, tungsten lamp located at least) cm. from the photosensitive layer. Thereafter, using a similar lamp, a uniform second radiation energy pattern is applied from transparent polyethylene film side to the whole surface for about I second to control the latent image. The controlled latent image was developed by a negative charged fine particle liquid developer to obtain a visible positive image at the photosensitive layer side and a reversed image at the supporting body side. These images were of very high contrast having no fog.

EXAMPLE 2 Ten gr. of TiO,, 2 gr. of alkyd resin (trade name Olester 301) and 13 ml. of toluene were mixed in a ball mill for about 4 hours. The mixture obtained is coated on semitransparent tracing paper having a thickness of 20p, to make a photoconductive body of TiO -alkyd series. The coating again had a thickness of from to 20 An original consisting of negative film was placed in close contact with the photosensitive layer of the electrophotosensitive material. A first radiation energy pattern, according to the light-and-dark pattern of the original, was applied to the photosensitive layer for about seconds by the tungsten lamp, similar to that mentioned above, to form an electrical latent image on the photosensitive layer. At the same time, a uniform second radiation energy pattern was applied for about 15 seconds to the supporting body to control the latent image. The controlled latent image was then developed by a negative charged fine particle liquid developer to obtain a visible positive image on the photosensitive layer side and a reversed image on the supporting body side. The image was not fogged and had high contrast.

EXAMPLE 3 Ten gr. of ZnO (made by SAKAI KAGAKU I(.K.), ml. of polyvinyl alcohol (PVA) aqueous solution 1 gr. PVA/IOO ml. pure water) were mixed in a ball mill for about 2 hours. The mixture formed was coated with a thickness of 10p. to 20p, on the transparent glass to obtain a photosensitive body of ZnO-PVA series. An original consisting of a negative film was placed in close contact with the support body. A first radiation energy pattern, according to the light-and-dark pattern of the original, was applied to the support body for about one-fifth of a second by the tungsten lamp mentioned above, to form an electrical latent image on the photosensitive layer. A uniform second radiation energy pattern was then applied to the photosensitive layer for about one-fifteenth second, by another tungsten lamp similar to the one above, to control the latent image. The controlled image was developed by a negative charged fine particle liquid developer to obtain a reversed image at the photosensitive layer side while a positive image was obtained at the supporting body side. Both of these visual images were without fog and had high contrast.

The second class of the present process is shown in FIGS. 7-12. In this process, a first radiation energy pattern is applied to a first surface of the electrophotosensitive material, e.g. the photosensitive layer or the supporting body, to fonn an electrical latent image on the photosensitive layer, and a second radiation energy pattern is applied to the same surface on which the latent image has been formed, to controlthe latent image.

In the second class of the process it has been experimentarily confirmed that when the amount of the energy (light intensity X time) of the first and second radiation energy patterns are suitably increased or decreased, the characteristics of the formed electrical latent image changes as the amount of energy crosses a critical value. This phenomenon manifests itself such that when the amount of energy is below the critical value, the same electrical latent image as obtained in the prior art process is obtained, however; when the amount of energy is over the critical value, a wholly opposite latent image is formed. The theoretical explanation of this phenomenon has not yet been established. However, a possible explanation is that when the radiation energy pat ern is applied t the photosensitive layer, a positive-negative charge polarization is produced on said layer due to the Dember effect or the internal polarization effect. If however, a great deal of energy is applied, the polarization proceeds further on one hand, but at the same time; and the previously polarized negative charge, which has a faster moving rate than that of positive charge, becomes active to bond with the positive charge, to produce depolarization. Consequently, at a certain amount of energy, the amounts of polarization and depolarization become balanced so that the photosensitive layer is substantially neutralized and there is no external field.

Accordingly, when a radiation energy pattern, according to the light-and-dark pattern of the original, is applied to the photosensitive layer in its initial state, negative-positive charge polarization is produced in the sections of the photosensitive layer corresponding to the light portion of the original. However, if much more energy is applied to the photosensitive layer, the section of the layer corresponding to the light portion of the original is neutralized, and the section of the photosensitive layer corresponding to the dark portion of the original is polarized because the amount of energy applied to this section is much less than that applied to the light section; hence, it has not reached the critical value. Consequently, by suitable adjustment of the magnitudes of the first and second radiation energy patterns, it is possible to optionally and selectively form a positive or reversed electrical latent image on the photosensitive layer with the critical value as the border area therebetween. It should be noted that the critical value varies with the substance constituting the photosensitive layer and it is, therefore, necessary to select a certain amount of energy suitable for the photosensitive layer used.

The above-mentioned phenomenon is present for cases where the first and second radiation energy patterns are the same pattern or where one of the first or second radiation energy patterns is a uniform energy pattern.

In the process of FIG. 7, as seen in FIG. 7-1, a first radiation energy pattern, according to the light-and-dark pattern of the original 4, which is in close contact with the photosensitive layer of the photosensitive body 3, is applied to the photosensitive layer by light source 10 to form an electrical latent image on the photosensitive layer. A second radiation energy pattern, having a magnitude which exceeds the critical value for reversing the latent image, is applied through the original 4 to the photosensitive layer so as to reverse said latent image. The reversed latent image is then developed and made visible by a charged fine particle developer. The charge states of each step are as shown in the respective figures of FIG. 7. In this embodiment, it may be assumed that the electrophotosensitive material 3 comprises a photosensitive layer of ZnO-alkyd resin coated on supporting body 2 which may be made of paper, synthetic resin film or a metallic plate and that the original 4 is a negative film in close contact with the photosensitive layer. A first radiation energy pattern is applied through the original 4 to the photosensitive layer 1 by a light source 10 to form thereon an electrical latent image. This light source may be a tungsten lamp, as previously described and located. When the energy is applied for a period less than 20 seconds and the formed latent image is developed by a liquid developer of negative charged fine particles, as seen in FIG. 7-2, the fine particles of the toner attach to the portions where the energy was applied, to thereby obtain a positive image. It was observed, that when the exposure was for a period of oneninetieth to 5 seconds, an especially high contrast positive image was obtained. When, however, the exposure time was for a period of 5 to 20 seconds, the contrast had deteriorated and an inferior positive image was obtained.

After the latent image had been formed, a second radiation energy pattern was applied to the photosensitive layer by the same light source 10 for a period of 20 seconds to reverse the latent image. The reversed image was then developed by the same developer. As seen in FIG. 7-3, fine particles of the toner selectively attached to the portions where the energy was not previously applied and thus a negative image 5 was obtained. In this case, when the exposure was made for about 40 seconds a good image was obtained, however, when it was made for a period of 20 to 40 seconds, only a low contrast image was obtained.

In the process of FIG. 8, as seen in FIG. 8-], a first radiation energy pattern, according to the light-and-dark portions of the original 4 is applied to the photosensitive layer 1 to form thereon an electrical latent image. Thereafter, as seen in FIG. 8-2, a uniform second radiation energy pattern is applied to the photosensitive layer to reverse the latent image. This reversed image was developed by a fine particle liquid developer and was as seen in FIG. 8-3. With this process, the

static charge patterns are obtained on the photosensitive body as shown in said figures. It may be assumed that the same electrophotosensitive material 3 as that used in the process of FIG. 7 is used in the instant embodiment. A first radiation energy pattern was applied to the photosensitive layer through the original 41, which is a negative film in close contact with the photosensitive layer I. The light source It) may be the same tungsten lamp specified above. When this embodiment was tested, the first radiation energy was applied for a period of slightly shorter than 20 seconds, the critical value to reverse the latent image. Thereafter, as seen in FIG. 8-2, the original l was removed and the image was reversed by the application of a uniform second radiation energy pattern for a period of about 3 seconds by a light source Ii, which may be the same as the light source 10 or different light source having less light intensity. As seen in FIG. 3-3, the reversed latent image was then developed by a negative charged fine particle developer to obtain the reversed negative image 5 In the process of FIG. 9, unlike the process of FIG. 8, a uniform first radiation energy pattern is first applied from the side of photosensitive layer of the electrophotosensitive material of FIG. 9-ll by a light source Ill to form an electrical latent image on the photosensitive layer. Thereafter, as seen in FIG. 9-2, the original 4 is placed in close contact with the photosensitive layer and a'ond raHiEKiFne'rg' pattern was applied through the original 4i to reverse the latent image, as shown in FIG. 9-3. The body was then developed to obtain visual image 5. in FIG. 9-3. In this process the same effect as in the case of FIG. 8 was expected and obtained.

In the process of FIG. Iii, as seen in FIG. Iii-ll, a first radiation energy pattern, according to the light-and-dark pattern of the original 4, is applied to the electrophotosensitive material from the side of the supporting body 2 to form an electrical latent image on the photosensitive layer ll. Thereafter, a

iii

tion energy pattern, according to the light-and-dark pattern of the original 4i, is applied from the side of the supporting body 2 of the electrophotosensitive material by the light source It) to form an electrical latent image on the photosensitive layer ll. Thereafter, as seen in FIG. 11-2, the original 4 is removed, and a uniform second radiation energy pattern is applied from the side of the supporting body by the light source 11 to reverse said latent image. This reversed latent image is developed by charged fine particles to obtain visual image 5 as shown in FIG. Ill-3.

in the process of FIG. 12, in contradistinction to the process of FIG. II, as seen in FIG. ll2-I, a uniform first radiation energy pattern is applied from the side of the supporting body 2 of the electrophotosensitive material 3 by the light source Ill to form an electrical latent image on the photosensitive layer. A second radiation energy pattern, according to the light-and- .darlc pattern of the original 4, is then applied from this same side to reverse said latent image. The process exhibits the same effect as in the process of FIG. iii. The charge states in these processes of FIG. Ill and I2 are as shown in the figures.

The relationship between the amounts of first and second energies to form a positive or reversed image according to the present process is explained with respect to the below-mentioned photosensitive materials.

PI-IOTOSENSITIVE MATERIALS USED I. Ten gr. of ZnO (SAKAI KAGAKU 1503), 0.3 gr. of alkyd resin (trade name Olester 301) and 13 ml. of toluene were mixed in a ball mill for 3 hours to obtain an emulsion. The obtained emulsion was uniformly coated, with a thickness of about 10 to 20p, on a base such as paper, aluminum plate or aluminum foil. This coating process was accomplished with 5 the aid of an iron bar wound with tungsten wire of I mm.

second radiation energy pattern, according to the original I light'and-dark pattern, is applied to the same surface as above for a period longer than the critical value to thereby reverse the latent image. The reversed image is developed by fine particle liquid developer to obtain visual image 5,, as shown in FIG. Iii-3i. in this process, the state of charge patterns are shown in the figures. According to this process, when the electrical latent image formed by the first radiation energy pattern is developed, the fine particle toner attaches to the portion where the light energy was not imparted (FIG. ll02) to obtain a negative image 5 This process differs from the process of FIG. 7 in that images in the relation of positive and negative are obtained.

40 III.

In the process of FIG. II, as seen in FIG. 11-11, a first radiadiameter with uniform pitch.

Ii. Tcn gr. of ZnO (SAIIAI KAGAKU I503) and 20 ml. of ethyl-alcohol is mixed in a ball mill for 2 hours. The obtained mixture is coated on the supporting body similar to that in I.

Ten gr. of ZnO (SAIKAI KAGAICU 1503) and 20 ml. of PVA aqueous solution (1 gr. PVA/IOI) ml. pure water) are mixed in a ball mill for about 2 hours. The obtained mixture is coated on the supporting body similar to that in I.

IV. On the photosensitive body obtained by II, an overlayer 45 of several microns thickness is coated by a PVA aqueous solution (I gr. PVA/IOO ml. pure water) to obtain a composite electrophotosensitive material.

The result obtainable in the present process using said four exemplified photosensitive bodies is shown in the following tables.

Electrophoto- 150 w. tungsten lamp located at 150 w. mercury lamp located at sensitive Process a distance of 40 cm. rom the a distance of 20 cm. from the mfltel'ial electrophotosensitive materiel electrophotosensitive materiel 1/90 see-10 sec. (positive image) 1/90 sea-3 sec. (positive image). FIG. 7 10 see-40 sec. 3 sec.20 sec).

Above 40 sec. (reversed lmage).. Above 20 sec. (reverse Image).

1/90 see-10 sec. (reversed irna e). 1/90 see-3 sec. (reversed image). FIG. 10 10 see-40 sec. (reversed Image X 3 see-20 see. (reversed imagefi I Above 40 sec. (positive image) Above 20 sec. (positive image).

Energy pattern (original). Energy pattern (original).

FIG. 8 or FIG. 9 Above 40 sec. (reversed Image) Above 20 sec. (reversed image).

Energy pattern (uniform) Energy pattern (uniform). Below 10 sec Below 5 sec.

Energy pattern (original) Energy pattern (ori nal) FIG. 11 or FIG. 12.. Above 40 sec. (positive image) Above 20 sec. (posit ve image).

Energy pattern (uniform) Energy pattern (uniform). Below 10 sec Below 5 see.

FIG. 1 1/90 sec.5 sec. (positive image)... 1/90 see-1 sec. (positive image). Above 20 sec. (reversed image) Above 10 sec. (reversed image).

FIG. 10 1/90 sea-5 sec. (reversed imege).. i/ sec.1sec. (reversed image). H Above 20 sec. (positive image). Above 10 sec. (positive image). III: Energy pattern (original) Energy pattern (original). IV FIG. 8 or FIG. 9 Above 10 sec. (reversed image). Above 3 sec. (reversed image).

Energy pattern (uniform) Energy pattern (uniform). Below 3 sec Below 1/15 sec.

Original pattern (original). Original pattern (original).

FIG. 11 or FIG. 12., .bove 10 sec. (positive Image)- Over 3 sec. (positive image).

nergy pattern (uniform) Energy ettern (uniform). Below 3 sec Below 1 15 sec.

In the foregoing processes an electrical latent image is formed by a first radiation energy pattern, and the latent image is controlled by a second radiation energy pattern. Consequently, when the controlled latent image is developed and made visible, a high contrast and fogless visual image is obtained. Furthermore, by adjusting the magnitudes of the first and second energies, a positive or reversed image is optionally and selectively obtained as certain critical amounts of energies are applied. Therefore, by using one polarity charged particle developer, a positive image (negative original-positive image) or a reversed image (negative original-negative image) is selectively obtained by the same process. Thus, it is no longer necessary to change the polarity of the developer and, therefore, the result is a simplified operation.

Throughout the specification, the terms positive image and reversed image have been used. The former was used to mean a positive image produced from a negative original. The latter was used to mean a negative image produced from a negative original. When, however, a positive original is used, a negative image is obtained instead of a positive image in normal case, and in a reversed case, a positive image is obtained from the positive original.

The present invention is not to be limited to the abovedescribed illustrative embodiments, but there are many modifications within the scope of the appended claims. The means for giving an original pattern to the electrophotosensitive material is especially not limited to the closely contacting penetrating system as shown in the drawing, but a projection system using an optical system may well be applicable.

Furthermore, not only penetrating printing is contemplated, but also close contact reflecting printing of the two surfaced original can be made by the present process. Finally, it is not necessary to provide the supporting body for the photosensitive body since a baseless photosensitive body can also be used as aforementioned.

We claim:

1. A chargeless electrophotographic printing process wherein an electrical latent image is formed on an electrophotosensitive element, selected from the group consisting of self-supporting photoconductive layers and photoconductive layers supported on a supporting base where the dark resistivity of the photoconductive layer is above IO'Q-cm. and the resistivity of any base is above tom-cm, the photoconductive layer including an inorganic electrophotoconductive material, by applying a light pattern of image configuration to a first surface of said element without separately imparting a charge thereto, which image is thereupon developed with the aid of a liquid developer including charged fine particles,

characterized in that the surface of said element opposite said first surface is exposed prior to the developing step to uniform light which is controlled such that the energy absorbed therefrom by the photoconductive layer is less than the energy absorbed by said photoconductive layer from said light pattern, any supporting base being sufficiently transparent to that light which is applied to its surface to allow penetration to said photoconductive layer.

2. A chargeless electrophotographic printing process according to claim I, wherein said exposure to uniform light is accomplished prior to the application of said light pattern to said electrophotosensitive element.

3. A chargeless electrophotographic printing process according to claim 1, wherein said exposure to uniform light is accomplished simultaneously with the application of said light pattern to said electrophotosensitive element.

4. A chargeless electrophotographic printing process according to claim 1, wherein said exposure to uniform light is accomplished after the application of said light pattern to said electrophotosensitive element.

5. A chargeless electrophotographic printing process according to claim 1, wherein said photoconductive layer is disposed on a supporting base which is transparent to said uniform light, and wherein said light pattern is applied to the surface of said photoconductive layer which is remote from said base while the uniform light is applied to the surface of the supporting base which is remote from said photoconductive layer.

-6. A chargeless electrophotographic printing process according to claim 5, wherein said supporting base has a thickness less thanSOu.

7. A chargeless electrophotographic printing process according to claim 1, wherein said photoconductive layer is disposed on a supporting base which is transparent to said light pattern, and wherein said light pattern is applied to the surface of said supporting base which is remote from said photoconductive layer while the uniform light is applied to the surface of the photoconductive layer which is remote from said base.

8. A chargeless electrophotographic printing process according to claim 7, wherein said supporting base has a thickness less than 9. A chargeless electrophotographic printing process wherein an electrical latent image is formed on an electrophotosensitive element, selected from the group consisting of self supporting photoconductive layers and photoconductive layers supported on a supporting base where the dark resistivity of the photoconductive layer is above IO'fl-cm. and the resistivity of any base is above l0flcm., the photoconductive layer including an inorganic electrophotoconductive material, by applying a light pattern of image configuration to a first surface of said element without separately imparting a charge thereto, which image is thereupon developed with the aid of a liquid developer including charged fine particles, characterized in that said first surface of said element is exposed prior to the developing step to uniform light which is controlled such that the energy absorbed therefrom by th photoconductive layer is less than the energy absorbed by said photoconductive layer from said light pattern thereby reversing the latent image that would otherwise have been formed, any supporting base being sufficiently transparent to said light, at least when said first surface is selected such that said light must pass through said base to reach said photoconductive layer, to allow penetration of said light to said photoconductive layer.

10. A chargeless electrophotographic printing process according to claim 9, wherein said exposure to uniform light is accomplished prior to the application of said light pattern to said electrophotosensitive element.

11. A chargeless electrophotographic printing process according to claim 9, wherein said exposure to uniform light is accomplished after the application of said light pattern to said electrophotosensitive element.

12. A chargeless electrophotographic printing process according to claim 9, wherein the photoconductive layer is disposed upon a supporting base, and wherein both said light pattern and said uniform light are applied to the surface of said photoconductive layer which is remote from said supporting base.

13, A chargeless electrophotographic printing process according to claim 9, wherein said electrophotosensitive element comprises a supporting base having a-thickness less than 80p" 14. A chargeless electrophotographic printing process wherein an electrical latent image is formed on an electrophotosensitive element, selected from the group consisting of self-supporting photoconductive layers and photoconductive layers supported on a supporting base where the dark resistivity of the photoconductive layer is above IOQ-cm. and the resistivity of any base is above l0Q-cm., the photoconductive layer including an inorganic electrophotoconductive material, by applying a light pattern of image configuration to a first surface of said element without separately imparting a charge thereto, which image is thereupon developed with the aid of a liquid developer including charged fine particles, characterized in that said light pattern is applied long enough to cause a reversal in the electric latent image relative to that which would be obtained with a shorter exposure to said light pattern, any supporting base being sufiiciently transparent to said light, at least when said first surface is selected such that said light must pass through said base to reach said photoconcording to claim 14, wherein said electrophotosensitive element comprises a supporting base on which said photoconductive layer is disposed, and wherein said light pattern is applied to the side of said supporting base remote from said photoconductive layer 17. A chargeless electrophotographic printing process according to claim 14, wherein said electrophotosensitive element comprises a supporting base having a thickness less than p. 

2. A chargeless electrophotographic printing process according to claim 1, wherein said exposure to uniform light is accomplished prior to the application of said light pattern to said electrophotosensitive element.
 3. A chargeless electrophotographic printing process according to claim 1, wherein said exposure to uniform light is accomplished simultaneously with the application of said light pattern to said electrophotosensitive element.
 4. A chargeless electrophotographic printing process according to claim 1, wherein said exposure to uniform light is accomplished after the application of said light pattern to said electrophotosensitive element.
 5. A chargeless electrophotographic printing process according to claim 1, wherein said photoconductive layer is disposed on a supporting base which is transparent to said uniform light, and wherein said light pattern is applied to the surface of said photoconductive layer which is remote from said base while the uniform light is applied to the surface of the supporting base which is remote from said photoconductive layer.
 6. A chargeless electrophotographic printing process according to claim 5, wherein said supporting base has a thickness less than 80 Mu .
 7. A chargeless electrophotographic printing process according to claim 1, wherein said photoconductive layer is disposed on a supporting base which is transparent to said light pattern, and wherein said light pattern is applied to the surface of said supporting base which is remote from said photoconductive layer while the uniform light is applied to the surface of the photoconductive layer which is remote from said base.
 8. A chargeless electrophotographic printing process according to claim 7, wherein said supporting base has a thickness less than 80 Mu .
 9. A chargeless electrophotographic printing process wherein an electrical latent image is formed on an electrophotosensitive element, selected from the group consisting of self supporting photoconductive layers and photoconductive layers supported on a supporting base where the dark resistivity of the photoconductive layer is above 109 Omega -cm. and the resistivity of any base is above 106 Omega cm., the photoconductive layer including an inorganic electrophotoconductive material, by applying a light pattern of image configuration to a first surface of said element without separately imparting a charge thereto, which iMage is thereupon developed with the aid of a liquid developer including charged fine particles, characterized in that said first surface of said element is exposed prior to the developing step to uniform light which is controlled such that the energy absorbed therefrom by the photoconductive layer is less than the energy absorbed by said photoconductive layer from said light pattern thereby reversing the latent image that would otherwise have been formed, any supporting base being sufficiently transparent to said light, at least when said first surface is selected such that said light must pass through said base to reach said photoconductive layer, to allow penetration of said light to said photoconductive layer.
 10. A chargeless electrophotographic printing process according to claim 9, wherein said exposure to uniform light is accomplished prior to the application of said light pattern to said electrophotosensitive element.
 11. A chargeless electrophotographic printing process according to claim 9, wherein said exposure to uniform light is accomplished after the application of said light pattern to said electrophotosensitive element.
 12. A chargeless electrophotographic printing process according to claim 9, wherein the photoconductive layer is disposed upon a supporting base, and wherein both said light pattern and said uniform light are applied to the surface of said photoconductive layer which is remote from said supporting base. 13, A chargeless electrophotographic printing process according to claim 9, wherein said electrophotosensitive element comprises a supporting base having a thickness less than 80 Mu .
 14. A chargeless electrophotographic printing process wherein an electrical latent image is formed on an electrophotosensitive element, selected from the group consisting of self-supporting photoconductive layers and photoconductive layers supported on a supporting base where the dark resistivity of the photoconductive layer is above 109 Omega -cm. and the resistivity of any base is above 106 Omega -cm., the photoconductive layer including an inorganic electrophotoconductive material, by applying a light pattern of image configuration to a first surface of said element without separately imparting a charge thereto, which image is thereupon developed with the aid of a liquid developer including charged fine particles, characterized in that said light pattern is applied long enough to cause a reversal in the electric latent image relative to that which would be obtained with a shorter exposure to said light pattern, any supporting base being sufficiently transparent to said light, at least when said first surface is selected such that said light must pass through said base to reach said photoconductive layer, to allow penetration of said light to said photoconductive layer.
 15. A chargeless electrophotographic printing process according to claim 14, wherein said electrophotosensitive element comprises a supporting base on which said photoconductive layer is disposed, and wherein said light pattern is applied to a surface of said photoconductive layer remote from said supporting base.
 16. A chargeless electrophotographic printing process according to claim 14, wherein said electrophotosensitive element comprises a supporting base on which said photoconductive layer is disposed, and wherein said light pattern is applied to the side of said supporting base remote from said photoconductive layer.
 17. A chargeless electrophotographic printing process according to claim 14, wherein said electrophotosensitive element comprises a supporting base having a thickness less than 80 Mu . 